Effects Of Coal-based Humic Acids On The Activity Of Arsenic In Soil And The Crop Growth

Adsorption-desorption experiment,soil column leaching experiment,and pot experiments were employed to study the effects of 11 coal-based humic acids on the adsorption and desorption,mobility,and Morphological distribution of As in calcic cinnoman soil and on the growth of maize(Zea mays)and rape(Brussicu campestris L.ssp)at seedling stage and on the adsorption and distribution of As in the plants of maize and rape.The result was hoped to provide the theory basis for using coal-base humic acids to repair arsenic contaminated soil.(1)The results of adsorption-desorption experiment showed that:The Change trend of adsorption and desorption quantities of different coal-based humic acid-soil systems to As were similar as the concentration of exogenous arsenic increased.The adsorption and desorption quantities increased as the concentration of exogenous arsenic increased,but the adsorption and desorption rates decreased as the concentration of exogenous arsenic increased.The 11 coal-based humic acids all increased the adsorptive action of the experimental soil to As.Both of the langmuir equation and freundlich equation nicely fitted the isothermal adsorption of different coal-based humic acid-soil systems to arsenic and the freundlich equation was better(R2 ?0.9748)than langmuir equation.In the range of experimental As concentration,the increases of maximum adsorption amount,adsorption rate,and MBC of soil added with No.10 of coal-based humic acid to As were the biggest and that of soil added with No.9 of coal-based humic acid to As were the minimum.Which was agreement with the adsorption capacity(K value)of the freundlich equation.Adsorption rate,desorption rate,and MBC were negatively correlated to the pH,CEC,and E4/E6 of coal-based humic acids..(2)The results of leaching experiment showed that:Arsenic was able to migrate downward in soil,but mobile ability was not big.The leaching ability of 10%KCl was stronger than that of deionized water.The As concentrations of leacheate in the treatments of No.8,9,and 11 of coal-based humic acids and EDTA were higher than that in As but the As concentrations of leacheate in the treatments of the other experimental coal-based humic acids were lower than that in As treatment.It showed that No.8,9,and 11 of coal-based humic acids increased the movement and activity of arsenic in soil and the promoting effect of No.9 of coal-based humic acid was the biggest and than the No.11 of coal-based humic acid.But the other experimental coal-based humic acids decreased the the movement and activity of arsenic in soil and the inhibiting effect of No.10 of coal-based humic acid was the biggest and than the No.6 of coal-based humic acid.The average concentrations of arsenic in both of first and second leacheates positively correlated to the pH,E4/E6,and CEC of the coal-based humic acids.(3)The results of pot experiment showed that:The quantities of different arsenic speciations from high to low were residual As>Fe-Mn oxides bound As>organic bound As>carbonate bound As>exchangeable As in the experimental soil.The different arsenic forms all increased in varying degrees as exogenous arsenic was added into the soil.The contents of exchangeable As and carbonate bound As both decreased and the contents of Fe-Mn oxides bound As,organic bound As,and residual As all increased when No.6 and 10 coal-based humic acids and exogenous arsenic were added into the soil.The contents of exchangeable As,carbonate bound As,Fe-Mn oxides bound As,and organic bound As all increased and the content of residual As reduced when No.9 and 11 of coal-based humic acids and exogenous arsenic were added into the soil.The contents of exchangeable As,carbonate bound As,and Fe-Mn oxides bound As all increased,especially the content of exchangeable As increased by 33.56%compared with the As treatment,and the contents of organic bound As and residual As reduced when EDTA and exogenous arsenic were added into the soil.,It also showed that No.6 and 10 coal-based humic acids decreased the activity of As and No.9 and 11 of coal-based humic acids increased the activity of As in the soil.The active effect of No.9 and 11 of coal-based humic acids on As was weaker than that of EDTA.The addition of exogenous arsenic significantly increased the content of available arsenic in the soil.The contents of arsenic in maize and rape plants were significantly positively correlated the content of available arsenic in the soil.Comparing with the treatment As,adding No.6 and 10 of coal-based humic acids reduced the content of available arsenic in the soil and decreased the absorption and accumulation of plants to arsenic.It also showed that No.6 and 10 of coal-based humic acids had inactivation on arsenic in the soil.But Adding No.9 and 11 of coal-based humic acids increased the content of available arsenic in the soil and promoted the absorption and accumulation of crops to arsenic.It also showed that No.9 and ? of coal-based humic acids had activation on arsenic in the soil,but the promoting effect was weaker than EDTA.The available arsenic content in the soil was significantly positively correlated to the pH,E4/E6,and CEC of the experimental coal-based humic acids.Adding exogenous arsenic significantly decreased the plant height,fresh plant weight,dry weights of shoot nad root of maize compared to treatment CK.But the effects of adding exogenous arsenic on the growth indicators above of rape were not significant compared to treatment CK.Adding exogenous arsenic also decreased the activity of antioxidant enzymes(POD,SOD,and CAT)in maize leaves.The activity of antioxidant enzymes(POD and CAT)reduced and the activity of SOD increased in rape leaves after adding exogenous arsenic.Adding exogenous arsenic increased the contents of proline and decreased the contents of chlorophyll in both of maize and rape leaves..Comparing to treatment As,adding coal-based humic acids promoted the growth of the experimental crops,increased the activity of antioxidant enzymes(POD,SOD and CAT)and the contents of chlorophyll in the leaves of the experimental crops,and reduced the contents of proline in the leaves of the experimental crops.Adding EDTA intensified the stress of exogenous arsenic on the crops and restrained the growth of the crops.Comparing to treatment As,the plant height,fresh plant weight,dry weights of shoot and root,the activity of antioxidant enzymes(POD,SOD and CAT),and the chlorophyll contents of the crops all decreased,,but the content of praline increased.Adding exogenous arsenic decreased the contents of OM,total N,and available K in the soil,but significantly increased the content of available P.Adding coal-based humic acids increased the contents of OM,total N,available P,and available K in the soil and promoted the absorption and accumulation of plants to N,P,and K.Especially,No.9 and 11 of coal-based humic acids significantly increased the contents of OM,total N,available P,and available K in the soil and promoted the absorption of the crops to them.Adding EDTA reduced the contents of OM,total N,available P,and available K in the soil and decreased the absorption and accumulation of the crops to them.